HPSC Assistant Professor Exam 2018
Which of the following is a correct statement of Hammond's postulate?
- (A) The transition state of an exothermic reaction will resemble the starting materials (reactants) more than the product.
- (B) The transition state of an exothermic reaction will resemble the products more than the starting materials (reactants).
- (C) The transition state of an endothermic reaction will resemble the starting materials (reactants) more than the product.
- (D) the difference in energy between the starting materials (reactants) and transition state controls the rate of a reaction.
Answer: (A) The transition state of an exothermic reaction will resemble the starting materials (reactants) more than the product.
Explanation: Hammond's Postulate relates the structure of a transition state to its energy. It states that the transition state structurally resembles the stable species (reactant or product) to which it is closer in energy.
- In an Exothermic Reaction, the transition state is energetically closer to the reactants. Thus, the TS resembles the starting materials (an "Early TS").
- In an Endothermic Reaction, the transition state is energetically closer to the products. Thus, the TS resembles the products (a "Late TS").